(HealthDay News) -- A single serving of leafy green vegetables each day may help keep dementia away, new research suggests.

Researchers evaluated the eating habits and mental ability of more than 950 older adults for an average of five years.

Those who consumed one or two servings of foods such as spinach, kale, mustard greens and/or collards daily experienced slower mental deterioration than those who ate no leafy greens at all, the study found.

The researchers "observed a protective benefit from just one serving per day of green leafy vegetables," which are known to be rich in vitamin K, added Morris, a nutritional epidemiologist at the Rush Alzheimer's Disease Center.

Morris was scheduled to present her team's findings Monday at the annual meeting of the American Society for Nutrition in Boston. Research presented at meetings is usually considered preliminary until published in a peer-reviewed medical journal.

"But while it's still being worked out, I'd say go to your local grocery and pick up some kale. There's certainly no harm done," she added.

For the study, funded by the U.S. National Institutes of Health, researchers focused on 954 men and women enrolled in Rush's Memory and Aging Project. Participants were 81 on average at the start, and three-quarters were women.

Every year for almost five years on average, participants completed a 144-item food and beverage questionnaire and underwent 19 mental skill tests.
In the end, each individual's nutrient intake was calculated based on the type and quantity of food consumed on a daily basis.

The team determined that those who routinely consumed one or two servings of leafy greens every day demonstrated the mental capacity of someone more than a decade younger, compared with those who never ate leafy greens.

The findings held up even after accounting for gender, age, education, smoking history, exercise, and any heightened Alzheimer's risk (such as a family history).

Might vitamin K supplements work as well?

Morris took a cautionary stance, noting that the study focused solely on food sources of vitamin K. She also suggested that the mental health benefit found in food sources might ultimately be associated with a constellation of nutrients found alongside vitamin K, rather than vitamin K alone.

"It is very difficult to tease apart the specific association of vitamin K from other nutrients," she said. Leafy greens also contain beneficial lutein, folate and beta-carotene, Morris added.

If you're not a fan of kale and spinach, such nutrients can also be found in a range of bright fruits and vegetables, the researchers pointed out.